To investigate the shear performance of the composite interface of concrete composite slabs with cross-shaped steel shear keys and perforated steel ribs, a total of 25 push-off specimens in 5 groups were designed and fabricated, with particular attention paid to two key factors: the configuration of the shear key (with or without foam filling) and interface cohesion (natural rough vs. artificial isolation). The push-off test results indicate that the cross-shaped steel shear key can significantly enhance both the shear capacity and ductility of the composite interface, with the peak load increased by approximately 112% compared to specimens without shear keys. Interface cohesion plays a decisive role in the shear performance, as the peak load of bonded specimens is approximately 1.57 to 1.65 times that of unbonded specimens. Filling the shear key with concrete can increase the peak load by 10% to 30%. Based on the experimental results, a three-dimensional nonlinear finite element model was established using ABAQUS for numerical simulation. The obtained load-slip curves show good agreement with the experimental results, with average errors of 2.36% for peak load and 4.62% for peak slip, thereby validating the effectiveness of the model. Parametric analysis reveals that increasing the thickness of the shear key yields limited improvement in bearing capacity (3%~9%), while increasing the friction coefficient of the slab surface can significantly enhance the residual bearing capacity (5%~15%), and improving the strength grade of the cast-in-place concrete can increase the bearing capacity by 15% to 26%. The research findings can provide a reference for the design and engineering application of new-type composite slabs.